The "fart tax" may rise again under a new name as New Zealand struggles to reduce its greenhouse gas emissions.

Methane, which accounts for about half of New Zealand's total annual greenhouse emissions, had to be brought under control, said panel members at last night's Hot Science event in Christchurch.

Discussing climate change and the winners and losers in Canterbury from changing land use, Lincoln University professor of resource economics Ross Cullen said the Government had to give clear signals that climate change was an important issue and that emissions behaviour had to change.

Although the Government had shelved earlier proposals for fart taxes on farmers and carbon taxes on business, one or both might still be necessary.

"We need to face up to the fact that we are producing a lot of greenhouse gases in New Zealand and we need to move away from that," Cullen said.

Moderator Kim Hill asked about the contributions to methane production from different rural sectors.

"Is it dairy farmers that produce the most methane? The cows, I mean?"

Cullen said the country's approximately 40 million sheep and six to seven million cattle produced about the same amount of methane.

Landcare Research global change processes science leader Dr David Whitehead said methane was the gas that could not be reduced.

"Clearly, farmers want to keep up production, increase production, and you can't reduce methane emissions unless you reduce the number of animals or the size of animals."

Hill said the need to keep production up seemed to be a "sacred cow".

People could make changes to reduce contributions to emissions, "but when it comes to production you have to keep pumping it out".

AgResearch chief scientist Dr Stephen Goldson said that, contrary to many people's beliefs and the description "fart tax", cattle and sheep burped rather than farted methane.

"Good lord," Hill said, "so it (a tax) could be resold to the farmers under a new name and they'll go, 'OK then'."

The final Hot Science public seminar next week looks at food production.